This invention relates to heat exchangers and particularly but not exclusively liquid-to-gas exchangers suitable for a variety of industrial purposes such as in dry-type natural-draught cooling towers of the kind commonly used in power stations in countries where water is scarce, and in the cooling of working places underground in deep-level mining.
An object of the invention is to provide a heat exchanger of this type which is assembled from a minimal number of basic components and which may yet be of substantial size and which lends itself to modular construction and assembly. These factors lead to relatively inexpensive manufacturing and installation costs and hence to superior economics, bearing in mind that in applications such as large modern cooling towers the cost of the heat exchangers is high.
A further object is to provide a fin-type heat exchanger which extensive testing has shown to be particularly and unexpectedly efficient, and to provide a range of parameters by which these results can be achieved.
In conventional heat exchangers of the type in question, the emphasis in the design has generally fallen either upon the lowering of the resistance to the passage of a fluid past the fins of the heat exchanger, thereby allowing large volumes of fluid to flow with no assistance from fans or with only a minimum of such assistance, or upon the opposed concept of maximising the heat transfer even at the expense of creating large-scale resistance to the flow of the fluid past the fins. Such resistance is commonly caused by excessive turbulence at the site of the fins.
The invention seeks to steer a different course to the extent that is based on the concept of utilising a controlled turbulence at the fins, so that laminar flow past the fins and the consequent build-up of heat transfer resistance in a stationary boundary layer is avoided but at the same time the resistance to flow is reduced to values which permit the passage of the fluid by natural flow in the case of a power station cooling tower or comparable installation.
With these objectives in view an extensive test program has been conducted on numerous types of heat exchanger to establish their characteristics, and in the course of these investigations it was discovered that there are certain critical relationships which, if present, lead to the optimised high-efficiency, low resistance features desired.
An initial phase of the test program gave rise to the filing of the Canadian patent application which has since been granted as Canadian Pat. No. 974,507, in which certain ranges of relationships were claimed.
The applicant has now discovered that the limits of the ranges in which the optimised performance mentioned earlier can be achieved are somewhat different from those disclosed in Canadian Pat. No. 974,507, and an object of this invention is to provide the parameters in this regard which the applicant has now established.